Luminous element and method for preparation thereof

ABSTRACT

A light-emitting element having at least a light-emitting region arranged between a pair of electrodes is provided, in which the light-emitting region contains either (A) a light-emitting material, a compound capable of sustaining the charge transport, and a heavy metal as a mixture, or (B) a compound that is capable of sustaining the charge transport and that includes both of a portion for contributing to the charge transport and a portion for contributing to the light emission within the compound, and a heavy metal as a mixture. A method for producing the light-emitting element, and a display device in which a plurality of the light-emitting elements are used, are provided also. With the light-emitting element of the present invention, it is possible to provide an organic thin film electroluminescent element that has a high emission efficiency, whose materials are easy to synthesize as compared with a heavy metal complex-doped element that has been studied widely in recent years, that has a small concentration quenching, and that is stable and uniform. Therefore, the light-emitting element of the present invention is applicable as a light source for use in a flat-panel-type self-luminous display device and for other various purposes such as communication and illumination.

TECHNICAL FIELD

The present invention relates to a thin film electroluminescent (EL)element such as, for instance, a self-luminous light-emitting element,which is suitable as a light source for use in a flat-panel-typeself-luminous display device and for other various purposes such ascommunication and illumination. It also relates to a method forproducing the same, and to a display device employing the same.

BACKGROUND ART

Recently, among flat-panel-type display devices, liquid crystal display(LCD) panels are used widely, but they still have problems such as a lowresponse speed, a narrow viewing angle, etc., and most of improvedversions of these also have problems such as insufficient properties andhigh costs of panels. Among these, thin film EL elements have drawnattention as new expected self-luminous light-emitting elements withexcellent visibility and high response speeds, which are expected to beapplicable in a wide range of fields. Particularly, various studies havebeen carried out about thin film EL elements having layers all of which,or a part of which, are made of organic materials that can be formedinto films by simple film forming processes such as vapor deposition orapplication at room temperature, which are called organic EL elements.This is because they are attractive due to, in addition to theabove-described characteristics, their production costs being reducibleto relatively low levels.

A thin film EL element that operates in a direct-current electric field(organic electroluminescent element, hereinafter referred to as “organicEL element” for short) has a light-emitting region present between apair of electrodes, that is, a hole-injection electrode and a cathode(electron-injection electrode), and achieves light emission byrecombination of an electron and a positive hole injected from theforegoing electrodes. Many studies have been made about such an organicEL element, but the emission efficiency thereof generally has been lowand they have been far from practical application in a light-emittingelement.

Among these, an element proposed by Tang et al. in 1987 (C. W. Tang andS. A. Vanslyke: Applied Physics Letter 51(1987)913 (issue date: Sep. 21,1987)) was an element having a hole-injection electrode, ahole-transport layer, a light-emitting layer, and a cathode that wereprovided on a transparent substrate in the stated order, in which indiumtin oxide (ITO) was used as the hole-injection electrode, a 75 nm-thickdiamine derivative layer was used as the hole-transport layer, and a 60nm-thick aluminum quinoline complex layer was used as a light-emittinglayer, and the cathode was made of a MgAg alloy that has both of theelectron-injection capability and the stability against the degradation.In addition to the improvement of the cathode, the use of diaminederivative excellent in transparency for forming the hole-transportlayer particularly allowed the hole-transport layer even with athickness of 75 nm to maintain sufficient transparency, and thisthickness made it possible to obtain a uniform thin film without a pinhole or the like. Therefore, this sufficiently reduced a total thicknessof an element including the light-emitting layer (to approximately 150nm), thereby allowing light emission with high luminance to be obtainedwith a relatively low voltage. More specifically, high luminance of notless than 1000 cd/m² and high efficiency of not less than 1.51 m/W wereobtained with a low voltage of not more than 10 V. This report by Tanget al. initiated active studies for the further improvement of thecathode, and the improvement of the element configuration such as theinsertion of an electron-injection layer and the insertion of thehole-injection layer, which have been continued to date.

The following will summarize a thin film EL (organic EL) element that isbeing studied generally.

To form respective layers of the element, a hole-injection electrode, ahole-transport layer, a light-emitting layer, and a cathode arelaminated in the stated order on a transparent substrate. Further, ahole-injection layer may be provided as required between thehole-injection electrode and the hole-transport layer, anelectron-transport layer may be provided as required between thelight-emitting layer and the cathode, or an electron-injection layer maybe provided as required on an interface with the cathode. Thus, bydividing and distributing functions to the respective layers,appropriate materials can be selected for the layers, respectively,thereby improving the characteristics of the element.

Generally, a glass substrate such as “CORNING 1737” (non-alkaliborosilicate glass produced by Corning Glass Works) is used widely asthe transparent substrate. The substrate preferably has a thickness ofapproximately 0.7 mm since this makes the substrate easy to handle fromthe viewpoint of strength and weight.

As the hole-injection electrode, a transparent electrode is used, suchas an ITO sputtered film, an ITO electron beam vapor deposition film, oran ITO ion-plating film. The thickness thereof is determined accordingto a sheet resistance and a visible light transmittance that arerequired, but in many cases it is set to be not less than 100 nm so asto decrease the sheet resistance, since a driving current density isrelatively high in an organic EL element.

For forming the hole-transport layer, a film obtained by vapordeposition of a diamine derivative is used widely, for instance, adiamine derivative used by Tang et al. such as

-   N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (hereinafter    referred to as TPD), or N,N′-bis(α-naphtyl)-N,N′-diphenylbenzidine    (hereinafter referred to as NPD). Particularly, a film obtained by    vapor deposition of a diamine derivative having a Q¹-G-Q² structure    disclosed in U.S. Pat. No. 4,539,507 (issue date: Sep. 3, 1985)    (corresponding to JP 2037475 B (JP 59-194399A (publication date:    Nov. 5, 1984)) is used widely. It should be noted that each of Q¹    and Q² is a group containing a nitrogen atom and at least three    carbocyclic rings (at least one of which is aromatic), and G is a    linking group composed of a cycloalkylene group, an arylene group,    an alkylene group, or a carbon-to carbon bond. These materials    generally have excellent transparency such that they are    substantially transparent even if it is formed into a film having a    thickness of approximately 80 nm, and have excellent film forming    properties. Therefore, by using the same, it is possible to form a    film without defects such as pin holes, and problems relating to the    reliability such as short-circuit hardly occur, even if a total    thickness of the element is reduced to approximately 100 nm.

The light-emitting layer also is, as reported by Tang et al., formed byvapor deposition of an electron-transport light-emitting material suchas tris(8-quinolinolato)aluminum so as to have a thickness of severaltens of nanometers. For achieving emitted lights of various colors, thelight-emitting layer is a relatively thin film, and in some cases, aso-called double hetero structure having an electron-transport layerwith a thickness of approximately 20 nm is used.

In many cases, the cathode used is a cathode made of an alloy such as aMgAg alloy or an AlLi alloy proposed by Tang et al., or a layeredcathode. The alloy forming the cathode is an alloy of a metal that has alow work function and a low electron-injection barrier and a metal thathas a relatively high work function and is stable. The layered cathodeis formed by laminating, for instance, an electron-injection layer ofvarious types such as LiF and aluminum.

Further, in addition to such a lamination configuration of“hole-transport layer/electron-transport light-emitting layer”, theconfiguration of “hole-transport light-emitting layer/electron-transportlayer”, and the configuration of “hole-transport layer/light-emittinglayer/electron-transport layer” are used widely. With use of any one ofthe lamination configuration, the same transparent substrate,hole-injection electrode, and cathode as those described above are usedin the same manner.

Generally, it is almost impossible to obtain organic compounds that haveexcellent electron transport capability, and relatively limitedcompounds can be used for forming the lamination configuration of“hole-transport layer/electron-transport light-emitting layer”. Incontrast, in the case of the configurations of “hole-transportlight-emitting layer/electron-transport layer” and “hole-transportlayer/light-emitting layer/electron-transport layer”, various types ofmaterials can be used for forming light-emitting layers. Therefore, theyhave possibilities for providing various colors of light and highperformance in the efficiency and the lifetime, and hold highexpectations.

For instance, U.S. Pat. No. 5,085,947 (issue date: Feb. 4, 1992)[corresponding to JP 2-250292A, date of publication: Oct. 8, 1990]discloses an element with a configuration of “hole-transportlight-emitting layer/electron-transport layer” in which

-   [4-{2-(naphthalen-1-yl)vinyl}phenyl]bis(4-methoxyphenyl)amine, or-   [4-(2,2-diphenylvinyl)phenyl]bis(4-methoxyphenyl)amine is used as a    hole-transport light-emitting material, and an oxadiazole derivative    is used for forming an electron-transport layer.

Further, WO 96/22273 (international publication date: Jul. 25, 1996)discloses an organic thin film EL element having a configuration of“hole-transport layer/light-emitting layer/electron-transport layer” inwhich 4,4′-bis(2,2-diphenyl-1-vinyl)-1,1′-biphenyl, which is ahole-transport light-emitting material, is used for forming alight-emitting layer.

Still further, in the Spring Annual Session G2.1 Lecture of MaterialResearch Society (MRS) in 1998 (oral presentation, Apr. 13, 1994), anelement was reported that has a configuration of “hole-injectionlayer/hole-transport light-emitting layer/hole blockinglayer/electron-transport layer” in which NPD, which is a compound of theQ¹-G-Q² type proposed by Tang et al., is used as a hole-transportlight-emitting material.

Thus, the use of not only an electron-transport light-emitting materialbut also a hole-transport light-emitting material as a light-emittingmaterial enables the designing with a wide-range of materials, andallows light emission with various colors to be obtained. However, itstill has not been possible to obtain those with sufficientcharacteristics regarding the emission efficiency and lifetime. Inparticular, it is said that in the case where a fluorescent material isused, only 25% of an excited state generated by recombination of anelectron and a hole contributes to light emission, and this has been asignificant problem in pursuing a further improved efficiency.

In such a situation, recently, many studies have been done about anelement in which a light-emitting layer obtained by doping a hostmaterial with a heavy metal complex, as disclosed in Applied PhysicsLetter, vol. 75, No. 1, pages 4 to 6 (issue date: Jul. 5, 1999). It isreported that in such an element, due to a heavy metal effect, a tripletexciton that is said to inherently make a forbidden transition andtherefore does not contribute to light emission is caused to make aluminescent transition to a ground state, thereby allowing the tripletexciton, which is said to be generated at a rate of 75%, to be used inlight emission. Therefore, the foregoing element can achieve a higherefficiency.

However, fac tris(2-phenylpyridine)iridium [abbreviated as “Ir(ppy)3”]disclosed in the foregoing thesis and many other heavy metal complexescannot necessarily be synthesized or purified easily. On the other hand,a layer made of a single material does not have a sufficient chargetransport capability, and exhibits significant concentration quenching(the decrease of the emission intensity at or above a certainconcentration). Therefore, it has been usual to use a charge transporthost material doped with a heavy metal complex at an appropriateconcentration, but the efficiency and the lifetime depend on the dopantconcentration, thereby causing disadvantages in the production.

Considering these conditions, the inventors of the present invention notonly designed heavy metal complex materials of various structures andstudied characteristics thereof in detail, but also studied a wide rangeof light-emitting elements in each of which a light-emitting layercontained a mixture of a heavy metal and a compound that were selectedfrom a variety of the same and that were deposited independently fromeach other. As a result, the inventors found the following. A heavymetal and a compound for contributing to light emission need not be onecompound as a complex. Even in the case where a compound forcontributing to light emission and a heavy metal physically were mixedand present close to each other, it was observed widely that theemission efficiency was improved significantly as compared with the casewhere no heavy metal was contained. With this, the present invention wascompleted. Further, the inventors also found that the emissionefficiency further improved in the case where the heavy metal mixedtherein was in as fine a state as possible. Thus, the present inventionwas completed.

SUMMARY OF THE INVENTION

More specifically, the light-emitting element of the present invention,the method for producing the same, and the display device employing thesame are as follows.

(1) A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting region containsa mixture of a light-emitting material; a compound capable of sustainingcharge transport; and a heavy metal.

(2) A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting region is madeof a mixture of a light-emitting material, a compound capable ofsustaining charge transport, and a heavy metal, the mixture beingobtained by simultaneously depositing the light-emitting material, thecompound, and the heavy metal.

(3) The light-emitting element according to the item (1) or (2),

wherein a content of the heavy metal in the light-emitting region is ina range of 0.1 mol % to 50 mol % with respect to the light-emittingmaterial.

(4) The light-emitting element according to the item (1) or (2), whereinthe heavy metal mixed is in an ultrafine particle state that is selectedfrom an atomic particle state and cluster particle states in which eachcluster particle has not more than ten atoms of the heavy metal onaverage.

(5) The light-emitting element according to the item (1) or (2), whereinthe heavy metal mixed is in an ultrafine particle state that is selectedfrom an atomic particle state and cluster particle states in which eachcluster particle has not more than five atoms of the heavy metal onaverage.

(6) A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting region containsa mixture of a compound that is capable of sustaining charge transportand that includes both of a portion for contributing charge transportand a portion for contributing to light emission within the compound;and a heavy metal.

(7) A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting region is madeof a mixture of a compound that is capable of sustaining chargetransport and that includes both of a portion for contributing chargetransport and a portion for contributing to light emission within thecompound; and a heavy metal, the mixture being obtained bysimultaneously depositing the compound and the heavy metal.

(8) The light-emitting element according to the item (6) or (7), whereinthe compound capable of sustaining the charge transport is ahole-transport light-emitting material that includes both of a portionfor contributing to the charge transport and a portion for contributingto the light emission within the compound.

(9) The light-emitting element according to the item (6) or (7), whereina content of the heavy metal in the light-emitting region is in a rangeof 0.1 mol % to 50 mol % with respect to the compound that is capable ofsustaining charge transport and that includes both of a portion forcontributing charge transport and a portion for contributing to lightemission within the compound.

(10) The light-emitting element according to the item (6) or (7),wherein the heavy metal mixed is in an ultrafine particle state that isselected from an atomic particle state and cluster particle states inwhich each cluster particle has not more than ten atoms of the heavymetal on average.

(11) The light-emitting element according to the item (6) or (7),wherein the heavy metal mixed is in an ultrafine particle state that isselected from an atomic particle state and cluster particle states inwhich each cluster particle has not more than five atoms of the heavymetal on average.

(12) A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting region containsa mixture of a light-emitting material; a compound capable of sustainingcharge transport; and a heavy metal, and the light-emitting regionexhibits an increased ratio of light emission with respect to arecombination of unit charges, as compared with the case where thelight-emitting region is made of a mixture of only a light-emittingmaterial and a compound capable of sustaining charge transport.

(13) A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting region containsa mixture of a compound that is capable of sustaining charge transportand that includes both of a portion for contributing charge transportand a portion for contributing to light emission within the compound;and a heavy metal, and the light-emitting region exhibits an increasedratio of light emission with respect to a recombination of unit charges,as compared with the case where the light-emitting region is made ofonly a compound that is capable of sustaining charge transport and thatincludes both of a portion for contributing charge transport and aportion for contributing to light emission within the compound.

(14) The light-emitting element according to the item (12) or (13),wherein the heavy metal mixed is in an ultrafine particle state that isselected from an atomic particle state and cluster particle states inwhich each cluster particle has not more than ten atoms of the heavymetal on average.

(15) The light-emitting element according to item (12) or (13), whereinthe heavy metal mixed is in an ultrafine particle state that is selectedfrom an atomic particle state and cluster particle states in which eachcluster particle has not more than five atoms of the heavy metal onaverage.

(16) The light-emitting element according to any one of items (1), (2),(6), (7), (12), and (13), wherein the heavy metal comprises a metal withan atomic number of not less than 57.

(17) A method for producing a light-emitting element having at least alight-emitting region between a pair of electrodes, the methodcomprising forming at least one layer in the light-emitting region bysimultaneously depositing a light-emitting material, a compound capableof sustaining charge transport, and a heavy metal.

(18) The method according to the item (17), wherein the deposition ofthe heavy metal is deposition via a cracking means.

(19) A method for producing a light-emitting element having at least alight-emitting region between a pair of electrodes, the methodcomprising forming at least one layer in the light-emitting region bysimultaneously depositing a compound that is capable of sustainingcharge transport and that includes both of a portion for contributingcharge transport and a portion for contributing to light emission withinthe compound, and a heavy metal.

(20) The method according to the item (19), wherein the deposition ofthe heavy metal is deposition via a cracking means.

(21) The light-emitting element according to any one of the items (17)to (20), wherein the heavy metal comprises a metal with an atomic numberof not less than 57.

(22) A display device employing a plurality of light-emitting elements,each of the light-emitting elements having at least a light-emittingregion between a pair of electrodes, wherein the light-emitting regionin each light-emitting element contains a mixture of: a light-emittingmaterial; a compound capable of sustaining charge transport; and a heavymetal.

(23) A display device employing a plurality of light-emitting elements,each of the light-emitting elements having at least a light-emittingregion between a pair of electrodes, wherein the light-emitting regionin each light-emitting element contains a mixture of a compound that iscapable of sustaining charge transport and that includes both of aportion for contributing charge transport and a portion for contributingto light emission within the compound; and a heavy metal.

(24) The display device according to the item (22) or (23), wherein theheavy metal mixed is in an ultrafine particle state that is selectedfrom an atomic particle state and cluster particle states in which eachcluster particle has not more than ten atoms of the heavy metal onaverage.

(25) The display device according to the item (22) or (23), wherein theheavy metal mixed is in an ultrafine particle state that is selectedfrom an atomic particle state and cluster particle states in which eachcluster particle has not more than five atoms of the heavy metal onaverage.

(26) The display device according to the item (22) or (23), wherein theheavy metal comprises a metal with an atomic number of not less than 57.

(27) A light-emitting element comprising an organic light-emitting layerthat contains a heavy metal as a substance mixed therein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an embodiment of anorganic thin film electroluminescent element as a light-emitting elementof the present invention.

FIG. 2 is a view of a reaction formula indicating the formylation of4-(anthracen-9-yl)phenyl-triphenyl-phenylenediamine as a result of aVilsmeier reaction.

DETAILED DESCRIPTION OF THE INVENTION

The following will describe a thin film EL element (organic EL element)according to an embodiment of the present invention.

A light-emitting element of the present invention has at least alight-emitting region arranged between a pair of electrodes. Here, alight-emitting element having “at least a light-emitting region arrangedbetween a pair of electrodes” is composed of at least a pair ofelectrodes and a light-emitting function layer arranged anywhere betweenthe foregoing electrodes. For instance, the element may be composed ofat least a hole-injection electrode, an electron-injection electrode onan opposite side to the hole-injection electrode, and a light-emittingfunction layer that is interposed directly or indirectly between theforegoing two electrodes. Here, the light-emitting function layer refersto not only a light-emitting layer that actually emits light, but also,generically, various configurations such as (1) “hole-transportlayer/electron-transport light-emitting layer”, (2) “hole-transportlight-emitting layer/electron-transport layer”, and (3) “hole-transportlayer/light-emitting layer/electron-transport layer” (it should be notedthat the light-emitting layer includes an electron-transportlight-emitting layer, a hole-transport light-emitting layer, etc.).

The “light-emitting region” described herein indicates a layer thatactually emits light, among the light-emitting function layer asdescribed above. In other words, it is the electron-transportlight-emitting layer in the case of (1), the hole-transportlight-emitting layer in the case of (2), or a portion corresponding tothe light-emitting layer in the case of (3).

The present invention is characterized in that a heavy metal is presentas a material mixed in the materials forming the light-emitting regionof the organic EL element.

The light-emitting region used in the present invention can beclassified in more detail into categories including, for instance, thefollowing types (A) and (B):

(A) a light-emitting region containing a mixture of

-   -   a light-emitting material (a);    -   a compound (b1) capable of sustaining the charge transport; and    -   a heavy metal (c);

and,

(B) a light-emitting region containing a mixture of

-   -   a compound (b2) that is capable of sustaining the charge        transport and that includes both of a portion for contributing        to the charge transport and a portion for contributing to the        light emission within the compound itself, and    -   a heavy metal (c).

It should be noted that in the case where a compound having a smallercharge transport function is used as the compound (b2) that is capableof sustaining the charge transport and that includes both of a portionfor contributing to the charge transport and a portion for contributingto the light emission within the compound itself, the compound (b1)capable of sustaining the charge transport may be used also incombination as required, so that the light-emitting region contains thecompound (b2), the compound (b1), and the heavy metal (c) as a mixture.

Among those described above, particularly the light-emitting region ofthe type (B) is preferable since in that case a film constituting thelight-emitting region can be formed uniformly in a large area at a highyield stably.

Regarding the compound (b1) in the light-emitting region of the type(A), the compound (b1) capable of sustaining charge transport does notemit light if it is used alone, which is a common technologicalknowledge about organic thin film EL elements. Therefore, the compound(b1) capable of sustaining charge transport is used in a state in whichthe compound (b1) as a host material is doped with a light-emittingmaterial (a) as a guest material, i.e., a dopant.

As the light-emitting material (a), a laser dye material or the like maybe used, which is used as a luminescent dye used in a light-emittinglayer of a normal organic EL element.

As compared with the foregoing compound, the compound (b2) that is usedin the light-emitting region of the foregoing type (B), that is capableof sustaining the charge transport, and that includes both of a portionfor contributing to the charge transport and a portion for contributingto the light emission within the compound itself, does not require theuse of the light-emitting material (a) in combination therewith, sincethe compound (b2) includes both of a portion for contributing to thelight emission, and further, that is capable of sustaining the chargetransport.

In both of the cases of the types (A) and (B), a light-emitting regionpreferably is formed with a film made of a mixture of the foregoingmaterials, which is formed by simultaneously depositing the foregoingmaterials composing the light-emitting region. Examples of thedepositing method used herein include vapor deposition, electron beam(EB) vapor deposition, sputtering, and ion plating. In the case wherethese components are deposited, it is preferable to deposit the heavymetal component through a cracking means, particularly so that the heavymetal is dispersed and mixed in the light-emitting region in a state ofparticles that are as fine as possible, or more preferably, atomic-levelheavy metal particles. Finer particles of the heavy material are morepreferable since the light-emitting element is allowed to have a higheremission efficiency.

The layers of the light-emitting element of the present invention maycomprise, as described above, a hole-injection electrode, ahole-transport layer, a light-emitting layer, and a cathode that arelayered on a transparent substrate in the stated order. Further, ahole-injection layer may be provided as required between thehole-injection electrode and the hole-transport layer, anelectron-transport layer may be provided as required between thelight-emitting layer and the cathode, and an electron-injection layermay be provided as required on an interface of the cathode. Stillfurther, in the present invention, a combination of the foregoing layershaving respective functions is referred to as a light-emitting functionlayer, and a layer that actually emits light in the light-emittingfunction layer is referred to as a light-emitting region, as describedabove. The layer that conventionally has been referred to as“light-emitting layer” usually is included in the light-emitting regionin the present invention.

As described above, in the present invention, a technique like that in anormal light-emitting element is applicable in which an appropriatetransparent or opaque substrate is used and the foregoing elementconfiguration described above is formed on the substrate. To get theemitted light out of the element, normally at least one of the pairedelectrodes is a transparent or at least semi-transparent electrode. Inthe case where the electrode on the substrate side is transparent orsemi-transparent, it is normal that a transparent or semi-transparentsubstrate is used. In the case where an opaque substrate is used, theelectrode provided on a side opposite to the substrate side is atransparent or semi-transparent electrode.

Anything may be used as the substrate as long as it is capable of carrya light-emitting element of the present invention thereon. In manycases, a glass substrate usually used in a thin film EL element is used,such as “Corning 1737” (a non-alkali borosilicate glass produced byCorning Glass Works). However, a resin film such as a polyester film maybe used also.

The thickness of the substrate is not limited particularly, but itpreferably is in a range of approximately 0.3 mm to 1.1 mm from theviewpoint of the strength and weight in the case where the substrate isa glass substrate. In the case where the substrate is a resin filmsubstrate, the thickness preferably is in a range of approximately 50 μmto 1 mm.

The hole-injection electrode in the present invention may be anyelectrode as long as it is capable of functioning as an anode so as toinject holes in the element, and in many cases, the hole-injectionelectrode is a transparent electrode. In such a case, an indium tinoxide (ITO) film is used generally, which is formed by sputtering,electron beam vapor deposition, ion plating, etc. for improving thetransparency thereof or reducing the resistivity thereof. The ITO filmis in many cases subjected to various finishing treatments forcontrolling the resistivity and the shape thereof. The film thicknessthereof is determined according to required sheet resistance and visibleradiation transmissivity, but in an organic EL element, which has arelatively high driving current density, a film having a thickness ofnot less than 100 nm is often used so as to reduce the sheet resistance.Examples that can be used for forming the hole-injection electrode ofthe present invention include, in addition to these normal ITO films,various improved transparent conductive layers such as “IDIXO” (atransparent electrode material produced by Idemitsu Kosan Co., Ltd.,which is made of indium oxide and a hexagonal layer compound made ofindium zinc oxide, and is expressed by a molecular formula (generalformula) of In₂O₃(ZnO)_(n) (where n is an integer of not less than 3without a particular upper limit, but generally it is not more than 100,preferably, not more than 10)). The examples also may include filmsobtained by coating a paint of a transparent conductive material inwhich a conductive powder is dispersed, or other electrodes may be used.

The light-emitting region in the present invention may be anything aslong as it emits light under a condition of the co-presence with a heavymetal. Considering the characteristics as a single compound, examplesused for forming the light-emitting region of the present inventioninclude various materials in a wide range including varioushole-transport light-emitting materials and electron-transportlight-emitting materials, as well as compounds conventionally used forforming a light-emitting layer of an organic EL element. Among these, amaterial particularly preferably used is a compound that is capable ofsustaining the charge transport, that includes both of a portion forcontributing to the charge transport and a portion contributing to thelight emission within the compound itself, and that excellentlyfunctions as a light-emitting layer even if the layer is made of thecompound alone. A material of the foregoing group forms a single layeras a light-emitting region (light-emitting layer), or preferably alight-emitting function layer in combination with the hole-transportlayer and the electron-transport layer, while it exhibits a notabletendency of significantly improving the emission efficiency when it isco-present with a heavy metal.

Particularly, when its molecular structure has a tetraphenylenediamineskeleton, a higher EL emission efficiency and a longer lifetime areachieved as compared with the triphenylamine dimer (such as TPD), whichgenerically is called a Q¹-G-Q² structure. Further, since the foregoingmolecular structure is asymmetric, molecules thereof hardly associatewith one another, whereby crystallization or aggregation of the samehardly occur. Thus, an element with superior durability and longlifetime can be realized. More specifically, a phenyl group directlybonded with one of the nitrogen atoms of tetraphenylenediamine as askeleton is substituted with a bulky group such as phenylstyryl,diphenylbutadienyl, anthryl, or the like, while a phenyl group directlybonded with the other nitrogen atom is either not substituted orsubstituted with an alkyl or alkoxy group and has a greaterintermolecular interaction as compared with the other one, whereby thehole transport capability is improved. By using such a compound, it ispossible to achieve not only a prolonged lifetime, but also an increasedemission efficiency in the case where the compound forms a non-dopedlight-emitting layer made of the compound alone. As a reason for this,it is considered that when molecules tend to associate with one another,the concentration quenching due to interaction between portionscontributing to the luminescent transition in each molecule is exhibitedstrongly. In particular, what was discovered by the present invention asa noticeable fact was that in the case of a compound of such a group,the co-presence with a heavy metal made it possible to achieve a furthernotably improved emission efficiency.

Still further, a compound whose molecular structure includes both of aportion for contributing to the luminescent transition and a portion forcontributing to the hole transport within the compound is capable ofsustaining sufficient charge transport and light emission at the sametime, and a notable effect can be recognized.

Specific examples of the foregoing compound, that is, the compound (b2)used in the light-emitting region of the type (B), include

-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (abbreviated as “PPDA-PS”),-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine    (abbreviated as “M2PPDA-PS”),-   (4-{[4-(2,2-diphenylvinyl)phenyl](4-(9-anthryl)phenyl)amino}phenyl)diphenylamine    (abbreviated as “PPDA-PS-A”), and-   (4-{[4-(2,2-diphenylvinyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine    (abbreviated as “PPDA-PS-AM”).

In the case where such a compound (b2) is used, which is capable ofsustaining the charge transport and that includes both of a portion forcontributing to the charge transport and a portion for contributing tothe light emission within the compound, a content of the heavy metal (c)in the light-emitting region preferably is in a range of 0.1 mol % to 50mol %, or more preferably, in a range of 0.5 mol % to 20 mol % withrespect to the compound (b2).

Still further, in the case where the light-emitting region is formedwithout using the above-described “compound that includes both of aportion for contributing to the charge transport and a portion forcontributing to the light emission within the compound”, a configurationof a mixture layer can be used in which the mixture layer is obtained byusing a generally-used charge transport material as a host material,doping the same with a generally-used luminescent dye by vaporco-deposition, and further, making a heavy metal co-present. Theabove-mentioned light-emitting region of the configuration (A) thatincludes a light-emitting material (a), a compound (b1) capable ofsustaining the charge transport, and a heavy metal (c) as a mixturecorresponds to this configuration.

Here, examples of the generally-used charge-transport material, that is,the material equivalent to the compound (b1), include varioushole-transport materials such as triphenylamine-based hole-transportmaterials like TPD and NPD described above, stilbene-based materials,and hydrazone-based materials. In addition to these, a variety ofelectron-transport materials including various metal complexes such asaluminum-quinolinol complexes, oxadiazole derivatives, and triazolederivatives can be used also. Furthermore,4,4′-bis(carbazol-9-yl)biphenyl (abbreviated as “CBP”) can be usedsuitably.

Still further, as the light-emitting material (a), variousgenerally-used luminescent dyes can be used. For example, a variety ofluminescent dyes such as coumarin derivatives, quinacridon derivatives,and phenoxazone derivatives can be used, or more widely, any one can beused as long as an emitted light with an intended wavelength can beobtained.

A ratio of the light-emitting material (a) and the compound (b1) capableof sustaining the charge transport preferably is (a):(b1)=1 mol:0.1 to1000 mol, or more preferably, (a):(b1)=1 mol:1 to 500 mol.

A content of the heavy metal (c) in such a light-emitting region of thetype (A) preferably is 0.1 mol % to 50 mol %, or more preferably, 0.5mol % to 20 mol %, with respect to the light-emitting material (a).

As the heavy metal of the present invention, any one can be used as longas it contributes to increasing the probability of causing a tripletexciton that inherently makes a forbidden transition to make aluminescent transition to the ground state due to a so-called heavymetal effect. According to the studies herein, an effect was recognizednotably in the case where the heavy metal was a metal with an atomicnumber of not less than 57. An upper limit to the atomic number of theheavy metal is not defined particularly, but generally, those withatomic numbers of not more than 85 are more easily handled. Among these,Ir, Au, and Pt are preferable.

As described above, to form the light-emitting region of the presentinvention, it is preferable to simultaneously deposit theabove-described respective materials to form the light-emitting regionby vapor co-deposition or the like so that the region is made of amixture of these materials. As the deposition method, it is possible touse vapor deposition, electron beam (EB) vapor deposition, sputtering,ion-plating, etc. In the case where these components are deposited, itis preferable to deposit the same through a cracking means, particularlyso that the heavy metal is dispersed and mixed in the light-emittingregion in a state of as fine particles as possible, or more preferably,atomic-level heavy metal particles.

The heavy metal does not sufficiently contribute to the improvement ofthe emission efficiency if in the light-emitting region it is present ina so-called large-size cluster state in which a plurality of atoms ofthe metal compose an aggregation. Therefore, in the case where the heavymetal is deposited by vapor deposition or another depositing method ofthose described above, the heavy metal is used in a state of beingcracked to as fine a particle as possible, even to an atomic level,whereby a high emission efficiency can be achieved. It is consideredthat ideally, the whole of the heavy metal is co-deposited in an atomicstate. Therefore, the deposition preferably is carried out through acracking means, for instance, by using an ion-plating device obtained bycombining a normal EB vapor deposition device with a plasma cracker. Inthe light-emitting element of the present invention, to obtainpreferable results, the size of the particles of the heavy metalpreferably is reduced to be as small as possible with a view toimproving the emission efficiency, for instance, so that atoms of theheavy metal included in one average cluster are not more than five onaverage, more preferably not more than three on average, further morepreferably not more than 1.5 on average.

In the present element, as for the other layers, usual hole-injectionlayer, hole-transport layer, and electron-transport layer selected fromwide ranges can be used. To form the hole-injection layer, a starburstamine derivative, an oligo amine derivative, or the like often is usedfor reducing the driving voltage by smoothing the roughness of the ITOsurface, the improvement of the hole injection efficiency, and the like,as well as for lengthening the lifetime, and the layer sometimes isreferred to as a buffer layer. To form the hole-transport layer, apartfrom the TPD or NPD described above, it is possible to use the same incombination with the technique in which a hole-transport material havinga relatively great molecular weight and having a poor stereo structure,which therefore tends to cause association if it remains as it is, isblended with a hole-transport material having a relatively smallmolecular weight and having a stereo structure so that excellentcharacteristics are achieved.

Here, examples of the “hole-transport material having a relatively greatmolecular weight and having a poor stereo structure, which thereforetends to cause association if it remains as it is” includetriphenylamine polymers such as

-   N,N′-bis(4′-diphenylamino-4-biphenylyl)-N,N′-diphenylbenzidine    (abbreviated as “TPT”), and examples of the “hole-transport material    having a relatively small molecular weight and having a stereo    structure” include stilbene-based compounds such as    4-N,N-diphenylamino-α-phenylstilbene (abbreviated as “PS”).    Additionally, various materials conventionally used in organic thin    film EL elements also can be used for forming blend-type    hole-transport layer.

To form the electron-transport layer, the metal complex-based materialsthat have been studied widely since Tang et al. usedtris(8-quinolinolato)aluminum can be used, as well as oxadiazolederivatives, triazole derivatives, and other materials are applicablealso.

To form the electron-injection electrode in the present invention, as inthe prior art described above, it is possible to use an alloy of a metalthat has a low work function and a low electron-injection barrier and ametal that has a relatively high work function and is stable, such as aMgAg alloy or an AlLi alloy proposed by Tang et al. Apart from that, anyone of cathodes of various types that have been reported generally, forinstance, a layered cathode of Li and Al, or a layered cathode of LiFand Al, can be used as the cathode.

It should be noted that the light-emitting element of the presentinvention is applicable in an information display device for displayingcharacters, marks, images, etc. in which a plurality of light-emittingelements are used, for instance, a flat-panel-type self-luminous displaydevice, as an alternative to the LCD panel. Examples of such a displaydevice include a device for displaying characters and marks, in whichsingle-color light-emitting elements arranged in a matrix so thatseveral or several tens of the same are arrayed in each of the verticaland horizontal directions form a unit for displaying one character, andseveral hundreds of the units in total are arranged in the vertical andhorizontal directions, which means that several tens of thousands toseveral hundreds of thousands of light emitting elements are arranged inthe whole display device. Examples of the same also include a colordisplay device in which a pixel is composed of light-emitting elementsof three colors of RGB (red, green, and blue), and the pixels arearranged in a matrix.

The inventions of the light-emitting elements of the above-describeditems (1), (6), (12), and (13) of the present invention have essentialcharacteristics in that in the light-emitting element including at leasta light-emitting region arranged between a pair of electrodes, thelight-emitting region contains a compound capable of sustaining thecharge transport (note: here, the combination of (a) and (b1) in theaforementioned type (A), and (b2) in the aforementioned type (B)generically are referred to as the compound capable of sustaining thecharge transport) and a heavy metal as a mixture. By containing thecompound that is capable of charge transport in a layer made of the samealone, the charge transport is continuously maintained, and theelectron-hole recombination is maintained in the light-emitting region,surroundings of the same, and on an interface thereof. Further, bycontaining a heavy metal along with the foregoing compound, a tripletexciton that inherently makes a forbidden transition is allowed to makea luminescent transition from an excited state to a ground state due toa so-called heavy metal effect. This allows the triplet exciton thatinherently does not contribute to light emission and that is generatedat a considerably high rate to be used for light emission, whereby asignificantly high emission efficiency can be achieved.

In the inventions of the light-emitting elements of the above-describeditems (2) and (7) of the present invention, the light-emitting region ismade of a mixture of a compound capable of sustaining charge transportand a heavy metal, the mixture being obtained by simultaneouslydepositing the foregoing component materials composing thelight-emitting region. Thus, by containing the compound that is capableof sustaining the charge transport in a layer made of the same alone,the charge transport is continuously maintained, and the electron-holerecombination is maintained in the light-emitting region, surroundingsof the same, and on an interface thereof. Further, by simultaneouslydepositing a heavy metal along with the foregoing compound so as to forma layer of the mixture of the materials, a triplet exciton thatinherently makes a forbidden transition is allowed to make a luminescenttransition from an excited state to a ground state due to a so-calledheavy metal effect. This allows the triplet exciton that inherently doesnot contribute to light emission and that is generated at a considerablyhigh rate to be used for light emission, whereby a significantly highemission efficiency can be achieved.

Particularly, in the case where, as in the items (6) and (7) describedabove, the compound (b2) that includes a portion for contributing to thecharge transport and a portion for contributing to the light emission inthe compound is used as the compound capable of sustaining the chargetransport is used in the light-emitting element of the presentinvention, it is possible to sustain sufficient charge transport andlight emission at the same time. This is preferable since a more notablyhigh emission efficiency can be achieved.

As in the item (8) described above, the light-emitting element of thepresent invention may be configured so that the compound capable ofsustaining the charge transport in the item (6) or (7) is ahole-transport light-emitting material. By so doing, it is possible tosustain sufficient charge transport and light emission at the same time.This is preferable since a more notably high emission efficiency can beachieved.

As in the items (3) and (9) described above, the light-emitting elementof the present invention may be configured so that a content of theheavy metal in the light-emitting region is in a range of 0.1 mol % to50 mol % with respect to the light-emitting material in the case of theitem (3), or so that a content of the heavy metal in the light-emittingregion is in a range of 0.1 mol % to 50 mol % with respect to thecompound that is capable of sustaining charge transport and thatincludes both of a portion for contributing charge transport and aportion for contributing to light emission within the compound, in thecase of the item (9). By so doing, it is possible to sustain sufficientcharge transport and light emission at the same time. This is preferablesince a more notably high emission efficiency can be achieved.

The inventions of the above-described items (16), (21), and (26) haveessential characteristics in that the heavy metal is a metal with anatomic number of not less than 57. This is preferable since theco-presence of a heavy metal with an atomic number of not less than 57with a compound makes it possible to achieve a high emission efficiency,even if the compound is a compound other than light-emitting materialsthat normally emit intense fluorescence or phosphorescence, for instancea compound capable of sustaining the charge transport or a compoundsthat includes a portion for contributing to the charge transport and aportion for contributing to the light emission.

In the inventions of the above-described items (4), (5), (10), (11),(14), (16), (24), and (25), the heavy metal mixed is present in a stateof particles as fine as possible in the light-emitting region, forinstance, in an ultrafine particle state that is selected from an atomicparticle state and cluster particle states in which each clusterparticle has not more than ten atoms of the heavy metal on average, orpreferably in an ultrafine particle state that is selected from anatomic particle state and cluster particle states in which each clusterparticle has not more than five atoms of the heavy metal on average.This is preferable since it improves the emission efficiency.

The following will describe the present invention in more detail whilereferring to specific examples thereof, but the present invention is notlimited to these specific examples. It should be noted that respectivelight-emitting materials, other than compounds whose manufacturers areshown specifically, were synthesized by usual methods as shown insynthesis examples herein, and were used after being purifiedsufficiently.

EXAMPLE 1

FIG. 1 is a schematic cross-sectional view illustrating an organic thinfilm electroluminescent element as a light-emitting element of thepresent invention. In FIG. 1, 1 denotes a transparent substrate. 2denotes a hole-injection electrode. 3 denotes a hole-transport layer. 4denotes a hole-transport light-emitting layer that corresponds to alight-emitting region in the present invention, that contains a compoundcapable of sustaining the charge transport and a heavy metal so that theheavy metal is co-present as a mixed material. 5 denotes anelectron-transport layer. 6 denotes a cathode. Light-emitting elementsof the other examples are substantially similar to this embodiment, butthe present invention is not limited to the embodiment shown in thedrawing.

The following describes the light-emitting element of the foregoingembodiment in more detail. A commercially-available ITO-applied glasssubstrate (produced by Sanyo Vacuum Industries Co., Ltd., size: 100mm×100 mm×0.7 mm (thickness), sheet resistance: approximately 14 Ω/□),was used as the substrate obtained by forming the hole-injectionelectrode 2 on the transparent substrate 1, and it was patterned byphotolithography so as to have a light-emitting area of portionsoverlapped with electron-injection electrodes of 1.4 mm×1.4 mm. Througha treatment applied to the substrate after the patterning byphotolithography, a resist was removed by immersing the substrate in acommercially-available resist remover (a solution of a mixture ofdimethyl sulfoxide and N-methyl-2-pyrolidone), and thereafter, thesubstrate was rinsed with acetone, and was immersed in fuming nitricacid for one minute so that the resist was removed completely. Thewashing of the ITO surface was carried out sufficiently on both of frontand back sides of the substrate, by carrying out mechanical abrasionwashing with a nylon brush while sufficiently supplying a 0.238 percentby weight (wt %) aqueous solution of tetramethyl ammonium hydroxide.Thereafter, the substrate was rinsed sufficiently with pure water, andwas subjected to spin drying. Then, the substrate was subjected tooxygen plasma treatment for one minute in a commercially availableplasma reactor (“PR41 type” produced by Yamato Scientific Co., Ltd.)under conditions of an oxygen flow rate of 20 sccm, a pressure of 26.66Pa (0.2 Torr), and a high frequency output of 300 W.

The substrate with the hole-injection electrode thus prepared wasarranged in a vacuum chamber. As a vapor deposition device, acommercially available high-vacuum vapor deposition device (“EBV-6DAtype” produced by ULVAC Inc.) was modified and used. It had, as a mainexhausting device, a turbo molecular pump of a pumping speed of 1500liter/min (“TC1500” produced by Osaka Vacuum, Ltd.), and achieved adegree of vacuum of not more than approximately 133.3×10⁻⁶ Pa(approximately 1×10⁻⁶ Torr). All the vapor deposition operations werecarried out in a range of 266.6 to 399.9×10⁻⁶ Pa (2 to 3×10⁻⁶ Torr). Asto all of the organic compounds, the vapor deposition operations werecarried out by connecting a direct current source (“PAK10-70A” producedby Kikusui Electronic Corp.) with a resistance-heating vapor depositionboat made of tungsten, and the vapor deposition of a heavy metal wascarried out using an ion plating device produced by combining acommercially-available electron beam (EB) vapor deposition source with aplasma cracker.

To form the hole-transport layer 3 on the substrate with thehole-injection electrode thus arranged in the vacuum chamber,N,N′-bis(4′-diphenylamino-4-biphenylyl)-N,N′-diphenylbenzidine(abbreviated as “TPT”, produced by Hodogaya Chemical Co., Ltd.) and4-N,N-diphenylamino-α-phenylstilbene (abbreviated as “PS”) wereco-deposited through vapor deposition at vapor deposition rates of 0.3(nm/sec) and 0.01 (nm/sec), respectively, whereby a blend-typehole-transport layer 3 was formed with a thickness of approximately 80nm.

Next, to form a hole-transport light-emitting layer corresponding to thelight-emitting region 4 of the present invention,

-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (abbreviated as “PPDA-PS”) and Ir were deposited at vapor deposition    rates of 0.3 nm/sec and 0.01 nm/sec, respectively, so as to have a    thickness of approximately 40 nm. Most of Ir dispersed and mixed in    the light-emitting region was dispersed and mixed as Ir in a single    atom state.

Here,

-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (abbreviated as “PPDA-PS”) was obtained by synthesis as follows.

41.4 g of N,N′-diphenyl-p-phenylenediamine, 66 g of iodobenzene, 100 mlof nitrobenzene, 45 g of K₂CO₃, 10.8 g of copper powder, and I₂ (trace)were put in a four-neck flask of 300-milliliter volume, and wererefluxed gently over 24 hours by stirring the same while removinggenerated water by reflux. Subsequently, steam distillation was carriedout, and when a distillate no longer came out, residues were filteredout after cooling, washed with water, and extracted using toluene. Afterremoving toluene by distillation, ethanol was added to the residues, andthe mixture was filtered. Recrystallization was carried out using asolvent of toluene and ethanol (toluene:ethanol=4:1 (by volume)),whereby 36.5 g of N,N,N′,N′-tetraphenyl-p-phenylenediamine was obtained.It had a melting point of 200° C. to 202° C.

Subsequently, 24 g (14 ml) of POCl₃ was dropped to a mixture of 24 g ofN-methylformanilide and 20 ml of o-dichlorobenzene in a four-neck flaskof 200-milliliter volume at 25° C. over 1 hour. Next, 36 g ofN,N,N′,N′-tetraphenyl-p-phenylenediamine obtained as above was addedthereto, and the mixture was stirred further for 2 hours at 90° C. to95° C. (since it was hardened midway, 30 ml of o-dichlorobenzene wasadded). The mixture was cooled after reaction, poured into 70 ml ofH₂SO₄ with a concentration of 10 percent by volume (vol %), and wasextracted using toluene. The toluene solution thus obtained was washedwith water, a 5 vol %-concentration Na₂CO₃ aqueous solution, and watersuccessively in this order, and was desiccated using Na₂SO₄. A productobtained after removing toluene by distillation was dissolved in a smallamount of toluene, and silica column chromatography was carried out.25.8 g of yellow-color crystal, which is

-   p-(N-phenyl-N-p′-N′,N′-diphenylaminophenyl)aminobenzaldehyde, was    obtained. It had a melting point of 136° C. to 138° C.

Subsequently, in a three-neck flask of 200 milliliter volume, 8 g ofdiethyl-1,1-diphenyl methyl phosphonate, and 13.3 g ofp-(N-phenyl-N-p′-N′,N′-diphenylaminophenyl)aminobenzaldehyde obtained asabove were dissolved in 80 ml of desiccated N,N-dimethyl formamide(DMF), and 3.5 g of potassium t-butoxide (t-BuOK) was added over 30minutes at 21° C. to 33° C. This was followed by stirring for 3.5 hoursat 20° C. to 25° C. Next, the solution was added to 300 ml of water withice while stirring. The toluene extraction and the washing with waterwere carried out, and after removing toluene by distillation, aluminacolumn chromatography was carried out using a toluene solvent. As aresult, 0.9 g of[4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine(abbreviated as “PPDA-PS”) was obtained. Here, mp was 218° C. to 219° C.

Next, to form the electron-transport layer 5,

-   tris(8-quinolinolato)aluminum (abbreviated as “Alq3”, produced by    Dojindo Laboratories) was deposited at a vapor deposition rate of    0.3 nm/sec so as to have a thickness of approximately 20 nm.

Subsequently, to form the cathode 6, from an AlLi alloy (produced byKojundo Chemical Laboratory Co., Ltd., Al/Li ratio by weight: 99/1),only Li was deposited at a low temperature at a vapor deposition rate ofapproximately 0.1 nm/s so as to have a thickness of approximately 1 nm.Then, the AlLi alloy was heated to a higher temperature so that theleaving of Li from the AlLi alloy stopped, and in this state, only Alwas deposited at a vapor deposition rate of approximately 1.5 nm/sec soas to have a thickness of approximately 100 nm. Thus, a layered cathodewas obtained.

After the vacuum chamber was filled with desiccated nitrogen, a lid madeof “Corning 7059 glass” (a non-alkali borosilicate glass produced byCorning Glass Works) was attached to the thin film EL element thusproduced, using an adhesive (Trade Name: “Super Vac Seal 953-7000”,produced by ANELVA Corporation) in the desiccated nitrogen atmosphere,so that the element became unsusceptible to an external atmosphere. Thusa sample of the thin film EL element was obtained.

The thin film EL element sample thus obtained was subjected to thefollowing evaluating operations.

The evaluation at an initial stage was made in a normal laboratoryenvironment of normal temperature and normal moisture when 12 hourselapsed after the attachment of the glass lid after the element wasobtained by vapor deposition, so as to determine the emission efficiency(cd/A), and the driving voltage for the emission of 1000 (cd/m²).Additionally, a continuous emission test was carried out with a currentvalue that caused an initial luminance to be 1000 (cd/m²), by theconstant DC driving, in a normal laboratory environment of normaltemperature and normal moisture. According to this test, a time when theluminance decreased to half (to 500 cd/m²) was determined as a lifetime.

A constant direct current supply (Trade Name: “Multichannel CurrentVoltage Controller TR-6163”, produced by ADVANTEST Corporation) was usedas a DC driving power source, so that voltage/current characteristicswere measured. The luminance was measured using a luminance meter (TradeName: “TOPCON Luminance Meter BM-8”, produced by TOPCON Corporation).Emission image qualities such as luminance irregularities, black points(non-emission portions), etc. were observed using an optical microscopewith a magnification of 50 times.

The pulse driving was carried out by a self-made constant current pulsedriving circuit, and the evaluation was made by setting the pulsefrequency to 100 Hz (10 ms), the duty to 1/240 (pulse amplitude: 42 μs),and the pulse waveform to a square waveform, while setting the pulsecurrent to various values. The luminance was measured using theluminance meter (Trade Name: “TOPCON Luminance Meter BM-8”, produced byTOPCON Corporation), and a pulse driving voltage that caused an averageluminance to become 270 (cd/m²). The continuous emission test wascarried out by continuous pulse driving in a normal laboratoryenvironment of normal temperature and normal moisture with a pulsevoltage that caused an initial luminance to be 270 (cd/m²). According tothis test, a time when the luminance decreased to half (to 135 cd/m²)was determined.

As to the states of the heavy metal particles mixed in thelight-emitting region such as the size of a cluster of the heavy metalmixed in the light-emitting region, that is, the number of atoms of theheavy metal contained in the cluster, whether the heavy metal isdispersed and mixed in a single atom state, etc., the transmissionelectron microscope observation, which is often used in a normal thinfilm analysis, was carried out after the film formation of thelight-emitting region, whereby the states of atoms of the heavy metalwere observed.

The evaluation results are shown in Table 1.

According to the present example, a thin film EL element was obtainedthat had a high emission efficiency, that achieved light emission withexcellent visibility by self generation at a low driving voltage, thatunderwent a small decrease in the luminance even in the continuousemission test, that did not have defects such as black points orluminance irregularities, and that could be used stably for asignificantly long period of time.

In particular, a thin film EL element was obtained that, even during thepulse driving corresponding to the actual driving in a panel, was drivenat a high efficiency with a low driving voltage, that underwent a smalldecrease in the luminance even in the continuous emission test, that didnot have defects such as black points or luminance irregularities, andthat could be used stably for a significantly long period of time.

EXAMPLE 2

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 1,

-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine    (abbreviated as “M2PPDA-PS”) was used in place of    [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (PPDA-PS).

Here,

-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine    (M2PPDA-PS) was obtained by synthesis as follows.

27.6 g of N,N′-diphenyl-p-phenylenediamine, 50 g of p-iodoanisole, 75 mlof nitrobenzene, 30 g of K₂CO₃, 7.2 g of copper powder, and I₂ (trace)were put in a four-neck flask of 300-milliliter volume, and wererefluxed gently over 24 hours by stirring the same while removinggenerated water by distillation. Subsequently, steam distillation wascarried out, and when a distillate no longer came out, residues wereextracted using toluene after cooling. After removing toluene bydistillation, residues were subjected to alumina column chromatographyusing a toluene solvent. After removing toluene by distillation,recrystallization of the residues was carried out using a solvent oftoluene and ethanol (toluene:ethanol=1:3 by volume), whereby 35.3 g of

-   N,N′-diphenyl-N,N′-bis(p-methoxyphenyl)-p-phenylenediamine was    obtained. It had a melting point of 132° C. to 134° C.

Subsequently, 20.4 g of POCl₃ (12 ml) was dropped to a mixture of 20.4 gof N-methylformanilide and 17 ml of o-dichlorobenzene in a four-neckflask of 200-milliliter volume over 1 hour at 25° C. Next, 35 g ofN,N′-diphenyl-N,N′-bis(p-methoxyphenyl)-p-phenylenediamine obtained asabove was added thereto, and the mixture was stirred further for 2 hoursat 90° C. to 95° C. The mixture was cooled after reaction. The reactionsolution was poured into 70 ml of 10 vol %-concentration H₂SO₄, and wasextracted using toluene. The toluene solution thus obtained was washedwith water, a 5 vol %-concentration Na₂CO₃ aqueous solution, and watersuccessively in this order, and was desiccated using Na₂SO₄. A productobtained after removing toluene by distillation was subjected to silicacolumn chromatography using a toluene solvent. After toluene was removedby distillation, residues were recrystallized using ethanol. 16.9 g oforange-color crystal, which is

-   p-[N-(p-methoxyphenyl)-N-{p-N′-phenyl-N′-(p-methoxyphenyl)aminophenyl}]-aminobenzaldehyde,    was obtained. It had a melting point of 160° C. to 161° C.

Subsequently, in a three-neck flask of 200 milliliter volume, 9.9 g ofdiethyl-1,1-diphenyl methyl phosphonate, and 16.4 g of

-   p-[N-(p-methoxyphenyl)-N-{p-N′-phenyl-N′-(p-methoxyphenyl)aminophenyl}]-aminobenzoaldehyde    obtained as above were dissolved in 65 ml of desiccated DMF, and 4.4    g of t-BuOK was added over 30 minutes at 21° C. to 33° C. This was    followed by stirring for 3.5 hours at 20° C. to 25° C. Next, the    solution was poured to 300 ml of water with ice while stirring. The    toluene extraction and the washing with water were carried out, and    after removing toluene by distillation, alumina column    chromatography was carried out using a toluene solvent. As a result,    0.7 g of-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine    (M2PPDA-PS) was obtained. It had a melting point of 271° C. to 272°    C.

A thin film EL element sample was produced in the same manner as that ofExample 1 except that the thus synthesized material was used as ahole-transport light-emitting material, and was co-deposited togetherwith Ir in the same manner as that of Example 1 so as to form thehole-transport light-emitting layer as a light-emitting region of thepresent invention, and the evaluating operations as those of Example 1described above were carried out. It should be noted that most of Irthat was dispersed and mixed in the light-emitting region was dispersedand mixed as Ir in a single atom state.

The evaluation results are shown in Table 1.

EXAMPLE 3

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 1,

-   (4-{[4-(2,2-diphenylvinyl)phenyl](4-(9-anthryl)phenyl)amino}phenyl)diphenylamine    (abbreviated as “PPDA-PS-A”) was used in place of-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (PPDA-PS), and it was co-deposited together with Ir in the same    manner as that of Example 1. The same evaluating operations were    carried out as those in Example 1 described above. The evaluation    results are shown in Table 1.

Here,

-   (4-{[4-(2,2-diphenylvinyl)phenyl](4-(9-anthryl)phenyl)amino}phenyl)diphenylamine    (PPDA-PS-A) was obtained by synthesis as follows.

After carrying out an Ullmann reaction of N-acetyl-1,4-phenylenediamineas a starting material with iodobenzene, a reaction product wassubjected to hydrolysis, and further subjected to an Ullmann reactionwith 9-(4-iodophenyl)anthracene, so that4-(anthracen-9-yl)phenyl-triphenyl-phenylenediamine was obtained.

Further, the formylation as indicated by the reaction formula shown inFIG. 2 was performed using a Vilsmeier reaction. It should be noted thatFIG. 2 is a reaction formula indicating the formylation of4-(anthracen-9-yl)phenyl-triphenyl-phenylenediamine through a Vilsmeierreaction. Many cases in which dimethyl formamide (DMF) was used toachieve a high reactivity in the formylation have been reported, but inorder to improve the reaction selectivity so as to increase a ratio of atarget substance to be obtained, N-methylformanilide was used. Since theVilsmeier reaction is an electrophilic addition reaction, a position Chaving the highest HOMO (highest occupied molecular orbital) electrondensity becomes a reaction position, and a position p of a benzene ringthat is bonded with N directly is formylated. A target substance wasextracted through sufficient isolation by column development.

Finally, diphenyl bromomethane and diethyl diphenylmethylphosphonateobtained from ethyl phosphate were used in a final reaction after theywere distilled under reduced pressure, and a diphenylvinyl group wasreacted with a formylated portion, as described above. A compound thusobtained further was subjected to sufficient isolation by columndevelopment, and was purified by sublimation sufficiently, before it wasused in the light-emitting element production.

Since it is considered that generally a vinyl bond is not resistant tohigh temperature in the Ullmann reaction, a synthesis example describedabove was such that preliminarily a skeleton was obtained by the Ullmannreaction and thereafter the formylation was carried out by the Vilsmeierreaction, and finally the diphenylvinyl group was added. However,another method is available in which a Pd catalyst or the like is usedand the coupling with the anthracene portion is carried out at the laststage, whereby the compound can be obtained at a higher yield. In thiscase, the same results were obtained regarding the light-emittingelement characteristics.

Further, most of Ir dispersed and mixed in the light-emitting region wasdispersed and mixed as Ir in a single atom state.

EXAMPLE 4

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 1,

-   (4-{[4-(2,2-diphenylvinyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine    (abbreviated as “PPDA-PS-AM”) was used in place of    [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (PPDA-PS), and it was co-deposited together with Ir in the same    manner as that of Example 1 described above. The same evaluating    operations were carried out as those in Example 1 described above.    The evaluation results are shown in Table 1.

Here,

-   (4-{[4-(2,2-diphenylvinyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine    (PPDA-PS-AM) was obtained by synthesis as follows.

The same synthesis as that in Example 3 was carried out except that10-(4-iodophenyl)-9-methoxyanthracene was used in place of9-(4-iodophenyl)anthracene used in Example 3. As the method forobtaining the compound, in addition to the above-described synthesis,another method is available in which a Pd catalyst or the like is usedand the coupling with the anthracene portion is carried out at the laststage, whereby the compound can be obtained at a higher yield. In thiscase also, the same results were obtained regarding the light-emittingelement characteristics.

Further, most of Ir dispersed and mixed in the light-emitting region wasdispersed and mixed as Ir in a single atom state.

EXAMPLE 5

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 3, Pt was used in place of Ir. The same evaluating operationswere carried out as those in Example 1 described above. It should benoted that most of Pt dispersed and mixed in the light-emitting regionwas dispersed and mixed as Pt in a single atom state.

The results are shown in Table 1.

EXAMPLE 6

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 3, Au was used in place of Ir. The same evaluating operationswere carried out as those in Example 1 described above. It should benoted that most of Au dispersed and mixed in the light-emitting regionwas dispersed and mixed as Au in a single atom state.

The results are shown in Table 1.

EXAMPLE 7

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 3, La was used in place of Ir. The same evaluating operationswere carried out as those in Example 1 described above. It should benoted that most of La dispersed and mixed in the light-emitting regionwas dispersed and mixed as La in a single atom state.

The results are shown in Table 1.

EXAMPLE 8

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 3, Tb was used in place of Ir. The same evaluating operationswere carried out as those in Example 1 described above. It should benoted that most of Tb dispersed and mixed in the light-emitting regionwas dispersed and mixed as Th in a single atom state.

The results are shown in Table 1.

EXAMPLE 9

A thin film EL element sample was produced in the same manner as that ofExample 1 except that the formation of the hole-transport light-emittinglayer of Example 1 was carried out as follows, and the same evaluatingoperations were carried out as those in Example 1 described above.

The results are shown in Table 1.

Here, the hole-transport light-emitting layer corresponding to thelight-emitting region of the present invention was formed in thefollowing manner.

4,4′-bis(carbazol-9-yl)biphenyl (abbreviated as “CBP”, produced byChemipro Kasei Kaisha, Ltd.) as a compound capable of sustaining thecharge transport,

-   [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethernyl]-4H-pyran-4-ylidene]propene-dinitrile    (abbreviated as “DCM2”, produced by Kodak Co., Ltd.) as a    light-emitting material, and Ir were deposited at vapor deposition    rates of 0.3 nm/sec, 0.01 nm/sec, and 0.01 nm/sec, respectively, so    as to form a film with a thickness of approximately 40 nm. The vapor    deposition of Ir was performed using an ion plating device produced    by combining an electron beam (EB) vapor deposition source with a    plasma cracker, as in Example 1.

It should be noted that most of Ir dispersed and mixed in thelight-emitting region was dispersed and mixed as Ir in a single atomstate.

COMPARATIVE EXAMPLE 1

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 1, only

-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (PPDA-PS) was used, without co-depositing Ir. The same evaluating    operations were carried out as those in Example 1 described above.

The evaluation results are shown in Table 1.

COMPARATIVE EXAMPLE 2

A thin film EL element sample was produced in the same manner as that ofExample 2 except that in forming the hole-transport light-emitting layerof Example 2, only

-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine    (M2PPDA-PS) was used, without co-depositing Ir. The same evaluating    operations were carried out as those in Example 1 described above.

The evaluation results are shown in Table 1.

COMPARATIVE EXAMPLE 3

A thin film EL element sample was produced in the same manner as that ofExample 1 except that in forming the hole-transport light-emitting layerof Example 1, Ba was used in place of Ir so as to be co-depositedtogether with

-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine    (PPDA-PS). The same evaluating operations were carried out as those    in Example 1 described above. The evaluation results are shown in    Table 1.

It should be noted that most of Ba dispersed and mixed in thelight-emitting region was dispersed and mixed as Ba in a single atomstate.

COMPARATIVE EXAMPLE 4

A thin film EL element sample was produced in the same manner as that ofExample 2 except that in forming the hole-transport light-emitting layerof Example 2, Ba was used in place of Ir so as to be co-depositedtogether with

-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine    (M2PPDA-PS) in the same manner as that of Example 2. The same    evaluating operations were carried out as those in Example 1    described above. The evaluation results are shown in Table 1.

It should be noted that most of Ba dispersed and mixed in thelight-emitting region was dispersed and mixed as Ba in a single atomstate.

COMPARATIVE EXAMPLE 5

A thin film EL element sample was produced in the same manner as that ofExample 9 except that in forming the hole-transport light-emitting layerof Example 9, only 4,4′-bis(carbazol-9-yl)biphenyl (CBP, produced byChemipro Kasei Kaisha, Ltd.), and

-   [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethernyl]-4H-pyran-4-ylidene]propene-dinitrile    (DCM2, produced by Kodak Co., Ltd.) were used, without co-depositing    Ir. The same evaluating operations were carried out as those in    Example 1 described above.

The evaluation results are shown in Table 1.

TABLE 1 Evaluation Results DC Constant Current Driving Pulse ConstantCurrent Driving Lifetime Lifetime (Time till (Time till LuminanceLuminance Others Sample Emission Driving decreases Emission Drivingdecreases (Luminance Sample Efficiency Voltage to half) EfficiencyVoltage to half) Irregularities, Number Contents (cd/A) (V) (hr) (cd/A)(V) (hr) etc.) Ex. 1 ITO/TPT + PS(80)/PPDA − PS + Ir(40)/ 18.4 8.0 250018.2 9.9 2100 Excellent Alq3(20)/Li/Al Ex. 2 ITO/TPT + PS(80)/M2PPDA −PS + Ir(40)/ 19.6 7.9 2700 19.3 10.1 2200 Excellent Alq3(20)/Li/Al Ex. 3ITO/TPT + PS(80)/PPDA − PS − A + Ir(40)/ 29.4 6.1 3100 25.1 8.2 2500Excellent Alq3(20)/Li/Al Ex. 4 ITO/TPT + PS(80)/PPDA − PS − AM + Ir(40)/28.7 5.9 3300 26.3 8.0 2600 Excellent Alq3(20)/Li/Al Ex. 5 ITO/TPT +PS(80)/PPDA − PS − A + Pt(40)/ 29.4 6.1 3100 25.1 8.2 2500 ExcellentAlq3(20)/Li/Al Ex. 6 ITO/TPT + PS(80)/PPDA − PS − A + Au(40)/ 30.4 6.13100 25.1 8.2 2500 Excellent Alq3(20)/Li/Al Ex. 7 ITO/TPT + PS(80)/PPDA− PS − A + La(40)/ 29.4 6.1 3100 25.1 8.2 2500 Excellent Alq3(20)/Li/AlEx. 8 ITO/TPT + PS(80)/PPDA − PS − A + Tb(40)/ 30.4 6.1 3100 25.1 8.22500 Excellent Alq3(20)/Li/Al Ex. 9 ITO/TPT + PS(80)/CBP + DCM2 +Ir(40)/ 6.4 7.2 2100 5.9 9.7 1900 Excellent Alq3(20)/Li/Al Comp.ITO/TPT + PS(80)/PPDA − PS(40)/ 8.4 8.0 2500 8.2 9.9 2100 Excellent Ex.1 Alq3(20)/Li/Al Comp. ITO/TPT + PS(80)/M2PPDA − PS(40)/ 9.6 7.9 27009.3 10.1 2200 Excellent Ex. 2 Alq3(20)/Li/Al Comp. ITO/TPT + PS(80)/PPDA− PS + Ba(40)/ 8.2 8.8 2000 7.9 10.6 1100 Excellent Ex. 3 Alq3(20)/Li/AlComp. ITO/TPT + PS(80)/M2PPDA − PS + Ba(40)/ 9.1 8.4 1900 9.0 12.1 1500Excellent Ex. 4 Alq3(20)/Li/Al Comp. ITO/TPT + PS(80)/CBP + DCM2(40)/2.1 7.9 1500 1.8 10.2 1200 Excellent Ex. 5 Alq3(20)/Li/Al

In Table 1, the element configurations of Examples of ComparativeExamples are described with abbreviations.

TPT represents

-   N,N′-bis(4′-diphenylamino-4-biphenylyl)-N,N′-diphenylbenzidine.

PS represents 4-N,N-diphenylamino-α-phenylstilbene.

PPDA-PS represents

-   [4-(2,2-diphenylvinyl)phenyl][4-(diphenylamino)phenyl]phenylamine.

M2PPDA-PS represents

-   [4-(2,2-diphenylvinyl)phenyl](4-methoxyphenyl){4-[(4-methoxyphenyl)phenylamino]phenyl}amine.

PPDA-PS-A represents

-   (4-{[4-(2,2-diphenylvinyl)phenyl](4-(9-anthryl)phenyl)amino}phenyl)diphenylamine.

PPDA-PS-AM represents

-   (4-{[4-(2,2-diphenylvinyl)phenyl][4-(10-methoxy(9-anthryl))phenyl]amino}phenyl)diphenylamine.

Alq3 represents tris(8-quinolinolato)aluminum.

CBP represents 4,4′-bis(carbazol-9-yl)biphenyl.

DCM2 represents

-   [2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethernyl]-4H-pyran-4-ylidene]propene-dinitrile.

Al represents aluminum.

Li represents lithium.

Ir represents iridium.

Pt represents platinum.

Au represents gold.

La represents lanthanum.

Tb represents terbium.

Ba represents barium.

The components constituting each layered configuration in an order fromthe ITO electrode side are thus described with the abbreviations fromleft, with slashes “/” being interposed therebetween. Numerical figuresin brackets “( )” indicate film thicknesses by nanometer, and “+”indicates that the film in which the components described on both sidesof the foregoing mark were co-present was formed by doping mixture orthe like.

INDUSTRIAL APPLICABILITY

So far the light-emitting element according to the present invention,the method for producing the same, and the display device using the samehave been described. The present invention provides a thin film ELelement that has a high emission efficiency, that does not undergodefects such as irregularities or black points, that achieves lightemission with excellent visibility by self generation at a low drivingvoltage, that undergoes a small decrease in the luminance even in acontinuous emission test, and that can be used stably for asignificantly long period of time with small power consumption. This ismade possible by configuring the light-emitting element having at leasta light-emitting region arranged between a pair of electrodes so that:

the light-emitting region contains either (A) a light-emitting material,a compound capable of sustaining the charge transport, and a heavy metalas a mixture, or (B) a compound that is capable of sustaining the chargetransport and that includes both of a portion for contributing to thecharge transport and a portion for contributing to the light emissionwithin the compound itself, as well as a heavy metal; or

in the foregoing case (A) or (B), each light-emitting region is composedof a layer made of the mixture of the foregoing materials bysimultaneously depositing the above-described constituent components.

Further, the present invention makes it possible to provide a thin filmEL element that requires only a low driving voltage and exhibits a highefficiency and high reliability, and that can be used stable for asignificantly long period of time with small power consumption, even inthe case of the pulse driving corresponding to the actual driving in apassive matrix panel.

The element may be configured so that:

more preferably, the compound capable of the charge transport includesboth of a portion for contributing to the charge transport and a portionfor contributing to the light emission within the compound;

more preferably, the compound is a hole-transport light-emittingmaterial;

more preferably, a content of the heavy metal in the light-emittingregion is not less than 0.1 mol % and not more than 50 mol % withrespect to either the light-emitting material or the compound thatincludes both of a portion for contributing to the charge transport anda portion for contributing to the light emission; or

more preferably, the heavy metal in the light-emitting region is mixedtherein in as fine a particle state as possible, for instance, in anultrafine particle state that is selected from an atomic particle stateand cluster particle states in which each cluster particle has not morethan ten atoms of the heavy metal on average, or further morepreferably, in an ultrafine particle state that is selected from anatomic particle state and cluster particle states in which each clusterparticle has not more than five atoms of the heavy metal on average.

In any one of these cases, the effects such as the improvement of theemission efficiency are exhibited more clearly.

Therefore, the present invention provides a useful thin film EL element,and the thin film EL element of the present invention can be used as alight source for use in a flat-panel-type self-luminous display deviceand for other various purposes such as communication and illumination.

1. A light-emitting element having at least a light-emitting regionbetween a pair of electrodes, wherein the light-emitting regioncomprises a mixture of: a light-emitting material; a compound capable ofsustaining charge transport; and a heavy metal in an ultrafine particlestate that is selected from an atomic particle state and clusterparticle states in which each cluster particle has not more than tenatoms of the heavy metal on average.
 2. A light-emitting element havingat least a light-emitting region between a pair of electrodes, whereinthe light-emitting region comprises a mixture of a light-emittingmaterial, a compound capable of sustaining charge transport, and a heavymetal in an ultrafine particle state that is selected from an atomicparticle state and cluster particle states in which each clusterparticle has not more than ten atoms of the heavy metal on average, themixture being obtained by simultaneously depositing the light-emittingmaterial, the compound, and die heavy metal.
 3. The light-emittingelement according to claim 1, wherein a content of the heavy metal inthe light-emitting region is in a range of 0.1 mol % to 50 mol % withrespect to the light-emitting material.
 4. The light-emitting elementaccording to claim 1, wherein the heavy metal mixed is in an ultrafineparticle state that is selected from an atomic particle state andcluster particle states in which each cluster particle has not more thanfive atoms of the heavy metal on average.
 5. A light-emitting elementhaving at least a light-emitting region between a pair of electrodes,wherein the light-emitting region comprises a mixture of: a compoundthat is capable of sustaining charge transport and that includes both ofa portion for contributing charge transport and a portion forcontributing to light emission within the compound; and a heavy metal inan ultrafine particle state that is selected from an atomic particlestate and cluster particle states in which each cluster particle has notmore than ten atoms of the heavy metal on average.
 6. A light-emittingelement having at least a light-emitting region between a pair ofelectrodes, wherein the light-emitting region comprises a mixture of: acompound that is capable of sustaining charge transport and thatincludes both of a portion for contributing charge transport and aportion for contributing to light emission within the compound; and aheavy metal in an ultrafine particle state that is selected from anatomic particle state and cluster particle states in which each clusterparticle has not more than ten atoms of the heavy metal on average, themixture being obtained by simultaneously depositing the compound and theheavy metal.
 7. The light-emitting element according to claim 5, whereinthe compound capable of sustaining the charge transport is ahole-transport light-emitting material that includes both of a portionfor contributing to the charge transport and a portion for contributingto the light emission within the compound.
 8. The light-emitting elementaccording to claim 5, wherein a content of the heavy metal in thelight-emitting region is in a range of 0.1 mol % to 50 mol % withrespect to the compound that is capable of sustaining charge transportand that includes both of a portion for contributing charge transportand a portion for contributing to light emission within the compound. 9.The light-emitting element according to claim 5, wherein the heavy metalmixed is in an ultrafine particle state that is selected from an atomicparticle state and cluster particle states in which each clusterparticle has not more than five atoms of the heavy metal on average. 10.A light-emitting element having at least a light-emitting region betweena pair of electrodes, wherein the light-emitting region contains amixture of: a light-emitting material; a compound capable of sustainingcharge transport; and a heavy metal in an ultrafine particle state thatis selected from an atomic particle state and cluster particle states inwhich each cluster particle has not more than ten atoms of the heavymetal on average, and the light-emitting region exhibits an increasedratio of light emission with respect to a recombination of unit charges,as compared with the case where the light-emitting region is made of amixture of only a light-emitting material and a compound capable ofsustaining charge transport.
 11. A light-emitting element having atleast a light-emitting region between a pair of electrodes, wherein thelight-emitting region contains a mixture of: a compound that is capableof sustaining charge transport and that includes both of a portion forcontributing charge transport and a portion for contributing to lightemission within the compound; and a heavy metal in an ultrafine particlestate that is selected from an atomic particle state and clusterparticle states in which each cluster particle has not more than tenatoms of the heavy metal on average, and the light-emitting regionexhibits an increased ratio of light emission with respect to arecombination of unit charges, as compared with the case where thelight-emitting region is made of only a compound that is capable ofsustaining charge transport and that includes both of a portion forcontributing charge transport and a portion for contributing to lightemission within the compound.
 12. The light-emitting element accordingto claim 10, wherein the heavy metal mixed is in an ultrafine particlestate that is selected from an atomic particle state and clusterparticle states in which each cluster particle has not more than fiveatoms of the heavy metal on average.
 13. The light-emitting elementaccording to claim 1, wherein the heavy metal comprises a metal with anatomic number of not less than
 57. 14. A method for producing alight-emitting element having at least a light-emitting region between apair of electrodes, the method comprising: forming at least one layer inthe light-emitting region by simultaneously depositing a light-emittingmaterial, a compound capable of sustaining charge transport, and a heavymetal, wherein the heavy metal is deposited through a means that cracksthe heavy metal.
 15. A method for producing a light-emitting elementhaving at least a light-emitting region between a pair of electrodes,the method comprising: forming at least one layer in the light-emittingregion by simultaneously depositing a compound that is capable ofsustaining charge transport and that includes both of a portion forcontributing charge transport and a portion for contributing to lightemission within the compound, and a heavy metal, wherein the heavy metalis deposited through a means that cracks the heavy metal.
 16. The methodfor producing a light-emitting element according to claim 14, whereinthe heavy metal comprises a metal with an atomic number of not less than57.
 17. A display device employing a plurality of light-emittingelements, each of the light-emitting elements having at least alight-emitting region between a pair of electrodes, wherein thelight-emitting region in each light-emitting element comprises a mixtureof: a light-emitting material; a compound capable of sustaining chargetransport; and a heavy metal in an ultrafine particle state that isselected from an atomic particle state and cluster particle states inwhich each cluster particle has not more than ten atoms of the heavymetal on average.
 18. A display device employing a plurality oflight-emitting elements, each of the light-emitting elements having atleast a light-emitting region between a pair of electrodes, wherein thelight-emitting region in each light-emitting element comprises a mixtureof: a compound that is capable of sustaining charge transport and thatincludes both of a portion for contributing charge transport and aportion for contributing to light emission within the compound; and aheavy metal in an ultrafine particle state that is selected from anatomic particle state and cluster particle states in which each clusterparticle has not more than ten atoms of the heavy metal on average. 19.The display device according to claim 17, wherein the heavy metal mixedis in an ultrafine particle state that is selected from an atomicparticle state and cluster particle states in which each clusterparticle has not more than five atoms of the heavy metal on average. 20.The display device according to claim 17, wherein the heavy metalcomprises a metal with an atomic number of not less than
 57. 21. Alight-emitting element comprising an organic light-emitting layer thatcontains a heavy metal as a substance mixed therein wherein the heavymetal mixed is in an ultrafine particle state that is selected from anatomic particle state and cluster particle states in which each clusterparticle has not more than ten atoms of the heavy metal on average.